* Renamed OAuth2Authentication to BearerAuthentication
* Added back OAuth2Authentication name
-there are libraries such as edx-enterprise that still import OAuth2Authentication. The OAuth2Authentication class should be fully removed when everything is importing BearerAuthentication correctly
- Removing deprecated auth classes
- Replacing OAuth2AuthenticationAllowInactiveUserDeprecated with OAuth2AuthenticationAllowInactiveUser
- the old class was a child class of a deprecated class that we are removing and replacing.
* Added new auth class
- Created new class called OAuth2AuthenticationAllowInactiveUser, which replaces old class with same name
- Renames previous OAuth2AuthenticationAllowInactiveUser to OAuth2AuthenticationAllowInactiveUserDeprecated
- Replaced all imports of OAuth2AuthenticationAllowInactiveUser to call deprecated class instead
- testing new class in discussion(added flag based on django setting)
Positive test case and improvements including: requires course id to be correctly encoded in the url params, only checks entitlements of the course in question, better source for the basket url, check enrollment upgrade deadline
